Voltammetric evidence for the presence of humic-like substances in fog water

Humic-like substances have recently become candidates for making up an important fraction of bulk organic carbon in various atmospheric samples. Their properties were exploited by various analytical — mostly spectroscopic — techniques. For lack of any decisive analytical evidence, their presence in the samples was proved only by comparison with arbitrarily selected humic or fulvic acid standards. This series of evidences requires as many independent principles of determination as possible to minimise false identification and to better characterise the properties of the bulk organic matter, which may also be important in various atmospheric processes. In this paper, we used anodic stripping voltammetry to characterise the complexing and electrochemical behaviour of organic matter in fog water under conditions prevalent in most surface waters. Although the method provided no quantitative information, important interference effects — formation of electrochemically labile complexes, adsorption on the working electrode, complex dissociation, etc. — were observed. Evaluation of the results revealed all of the major electrochemical attributes of natural complexants as had been reported for humic or fulvic acids. These may provide indirect evidence that natural complexants similar to humic or fulvic acids are present in fog water in concentrations sufficiently large to produce these effects. This finding, which supplements previous independent measurements, may be useful in assessing the sources and effects of humic-like substances in atmospheric samples.